In the current freshet of rainforest books, Yolen's rises to the surface not as a mere tour guide, but a gracious host to earth's ``dark green, / light green, / emerald green / bright green / copper green, / blue green, / ever-new green house.'' The author's atmosphere-laden free verse, which falls into unexpected, pleasing rhyme and repetition, correlates with Regan's sumptuous gouache artwork. While the text focuses on the relentless noise of forest inhabitants, borderless, painterly illustrations seem to spill off the pages in their intricate depictions of animals cavorting amidst tropical flora. The illustrations are just literal enough--allowing youngsters to match familiar and unknown species with names in the text. Yolen's language begs for reading aloud but for a common problem: her generous use of onomatopoetic translation of animal calls and other sounds may be difficult for readers to imitate without jarring the beauty and rhythm of the language. A stimulating challenge, however, in a strikingly vibrant package. Ages 4-8. (Apr.)